Using orthogonal pairs of rollers on concave beds (OPRCB) as a base isolation system—part I: analytical,experimental and numerical studies of OPRCB isolators

A somehow new isolating system is introduced for short‐ to mid‐rise buildings. It does not need high technology for manufacturing and is not costly, contrary to other existing systems like lead‐rubber bearing or friction pendulum bearing systems. Each isolator of the proposed system consists of two Orthogonal Pairs of Rollers on Concave Beds (OPRCB). Rolling rods installed in two orthogonal directions make possible the movement of the superstructure in all horizontal directions. The concave beds, in addition to giving the system both restoring and re‐centring capabilities, make the force–displacement behaviour of the isolators to be of hardening type. The results of the studies on the specifications of the proposed isolating system and its application to buildings can be presented in two parts. Part I relates to the analytical formulations and the results of experimental and numerical studies of the system's mechanical feature, including its dynamical properties, and part II focuses on the effectiveness of the proposed isolation system in seismic response reduction of low‐ to mid‐rise buildings. In part I of the work, presented in this paper, at first general features of the OPRCB isolator are explained and the analytical formulation, governing its dynamic motion, is derived and discussed in detail. Then, the results of experimental and numerical investigations, including the lateral load displacement relationship of the OPRCB isolators under various vertical loads, obtained by both Finite Element Analyses (FEA) and laboratory tests are presented (FEA results have been verified by the laboratory tests). Finally, responses of some Single Degree of Freedom (SDOF) systems, isolated by OPRCB devices, subjected to simultaneous effect of horizontal and vertical ground motions, are presented and compared with responses of their fixed‐base counterparts. Based on the numerical calculations, it is observed that the oscillation period of the isolated SDOF system is independent of its mass, the initial amplitude of its free vibration response and the value of rolling resistance coefficient. With regard to seismic response reduction it is seen that the amount of absolute accelerations in the SDOF systems, isolated by OPRCB devices, can be reduced drastically in comparison with the fixed‐base systems. Results also show that if the rollers and cylindrical beds are made of high‐strength steel materials, the system can be used effectively under the vertical loads of about the axial forces of ground floor columns in ordinary buildings up to 14 storeys. Copyright © 2010 John Wiley & Sons, Ltd.     

Effectiveness of sliding isolators with variable curvature in near‐fault ground motions

Recent studies have revealed that a sliding isolator with variable curvature (SIVC) can mitigate the resonance phenomenon likely to occur in seismic response of a conventional friction pendulum system (FPS) isolator due to its constant isolation frequency. The present study simulates four SIVC isolators and an FPS to find the optimum range of initial isolation period and coefficient of friction and employ them in comparing the effectiveness of SIVC in different peak ground acceleration (PGA) scales of near‐fault earthquakes. Velocity‐dependent coefficient of friction and modified viscoplasticity model have been used to simulate nonlinear friction force of the isolators. Results indicate identical performance of all SIVC isolators in PGA scales up to 0.4 g. When subjected to PGA scales from 0.4 g to 1.0 g, polynomial friction pendulum isolator (PFPI) and variable curvature friction pendulum system (VCFPS) reduce base displacement greatly, while conical friction pendulum isolator (CFPI) and variable frequency pendulum isolator (VFPI) show amplified responses. However, in mitigating structural acceleration, performance of CFPI and VFPI, unlike PFPI and VCFPS, which perform poorly, is excellent. Thus, in a strong near‐fault earthquake, PFPI and VCFPS or CFPI and VFPI can be chosen based on whether reduction of base displacement or super‐structural acceleration is the main concern of designer, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Wind‐induced inter‐story drift analysis and equivalent static wind load for multiple targets of tall buildings

In super high‐rise buildings with varying story heights, the wind‐induced inter‐story drifts might violate the specified limit. However, these effects have seldom been concerned in wind‐induced response analysis. The theory and application of equivalent static wind load (ESWL) for wind‐induced inter‐story drifts of super high‐rise buildings were studied in this paper. A spectral decomposition method suitable for multi‐point excitation problems was firstly proposed. The formula of ESWL targeting for largest inter‐story drift was derived. For more reasonable structural design, the ESWL for multiple targets including displacement atop of building and inter‐story drifts at all story levels is put forward, in which the dominant modal inertial forces are adopted as the based load vectors. The presented methods were finally verified by its application for the wind‐induced response analysis for a tallest super tall building in Guangzhou. The researched results showed that the proposed spectral decomposition method not only has the same precision as the complete quadratic combination method but also possesses higher computation efficiency. The ESWL for multiple targets produces the same static responses for all the specified wind‐induced response, so it is much more rational for wind‐resistant structural design. Meanwhile, it is more reasonable to select the wind‐induced responses in the same direction simultaneously as the targeted values for obtaining the required ESWLs; however, the ESWL targeting for the wind‐induced responses in all degrees of freedom would generate more queer and unrealistic ESWLs distribution. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance of variable curvature sliding isolators in base‐isolated benchmark building

The performances of variable curvature sliding isolators like variable frequency pendulum isolator (VFPI) and variable curvature friction pendulum system (VCFPS) installed in the base‐isolated benchmark building subjected to bi‐directionally acting seven strong earthquakes have been studied. The shear type base‐isolated benchmark building is modelled as three‐dimensional linear elastic structure having three degrees‐of‐freedom at each floor level. Time domain dynamic analysis of the building has been carried out with the help of constant average acceleration Newmark‐Beta method and non‐linear isolation forces has been taken care by fourth‐order Runge‐Kutta method. The force‐displacement responses of the VFPI and VCFPS are studied under parametric variations of their key characteristics for the comparative performance evaluation. The time history variations of response characteristics and peak response evaluation criteria are also investigated for overall comparison of their performances. The performance of VFPI and VCFPS are observed both in uniform and hybrid isolation systems. The force‐displacement responses of both VFPI and VCFPS subjected to strong near‐field earthquakes show excessively large isolator displacements at higher initial radii of curvature of sliding surface. The large isolator displacements of VFPI and VCFPS can be restrained efficiently by addition of viscous fluid dampers in comparison to the increase in coefficient of friction of isolators. Copyright © 2010 John Wiley & Sons, Ltd.     

A generalized method for estimating drifts and drift components of tall buildings under lateral loading

A generalized method for estimating the drifts of tall buildings composed of planar moment‐resisting frames and coupled shear walls under lateral loading is presented. This method establishes the stiffness equations at the story levels by assuming that all the nodes in the same floor of a planar lateral‐force‐resisting unit have an identical lateral displacement, an identical rotation component due to the axial deformations of the columns, and an identical rotation component due to the flexural and shear deformations of the beams. By adopting this simplification, the story drifts contributed by different types of deformations, namely, the axial deformations of the columns or wall piers, the flexural and shear deformations of the beams, and the double‐curvature bending and shear deformations of the columns or wall piers, can be identified. In the formulation of the stiffness matrix, the P‐Delta effects were also incorporated. Through comparisons between the lateral displacements and story drifts computed using the proposed method and those computed using the structural analysis software Midas/Gen, the proposed method is proved to have high accuracy in estimating the drifts of tall building structures.     

Testing facility for experimental evaluation of non‐structural components under full‐scale floor motions

The seismic vulnerability of non‐structural components and equipment with their expensive recovery and/or replacement costs has been demonstrated during past earthquakes. With the exception of the nuclear industry, the limited data collected from past earthquakes are not sufficient to completely characterize the seismic behaviour of non‐structural components and to develop effective mitigation measures. To address these limitations, the University at Buffalo has commissioned a dedicated non‐structural component simulator (University at Buffalo non‐structural component simulator (UB‐NCS)) composed of a two‐level testing frame capable of simultaneously subjecting both displacement and acceleration‐sensitive non‐structural components to realistic full‐scale floor motions expected within multi‐storey buildings. Current codes now require seismic qualification of important non‐structural components, and protocols for experimental qualification have been developed considering existing laboratory limitations. The new testing capabilities provided by the UB‐NCS are described to demonstrate the improved and more realistic qualification procedures that can be achieved. Results are presented from a test on two parallel partition walls aimed to verify the capabilities of the UB‐NCS. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of a high‐rise steel structure with viscous damped outriggers

Damped outriggers for tall buildings draw increasingly attentions to engineers. With a shaking table test, two models of a high‐rise steel column‐tube structure are established, one with outriggers fixed to the core and hinged at the columns, whereas the other's cantilevering outriggers are connected to columns by viscous dampers. According to their dynamic properties, five earthquake waves are selected from the Ground Motion Database of Pacific Earthquake Engineering Research Center (PEER), and two artificial waves are generated by software SIMQKE_GR. Under various peak ground accelerations (PGAs), nonlinear time‐history analysis is applied to compare structural elastic seismic responses, including accelerations, inter‐story drifts, base shear force, damper's response and additional damping ratios. It is concluded that under minor earthquakes, accelerations, inter‐story drifts and base shear force of structure with damped outriggers are larger than or nearly equal to those of the one with fixed outriggers, and the viscous dampers hardly work. But as PGA increases, the contrary situation happens, and the effect of viscous dampers is enhanced as well. The additional damping ratio reaches around 4% under mega earthquakes. Copyright © 2013 John Wiley & Sons, Ltd.     

An inter‐story drift‐based parameter analysis of the optimal location of outriggers in tall buildings

Outriggers are usually added in structural systems of tall buildings to collaborate central shear walls with peripheral columns. With outriggers, the structural overturning moment can be balanced, and the inter‐story drift can be controlled under horizontal loads. Therefore, the optimal location of outriggers plays a very important role in controlling the behavior of the whole building. Existing research has focused on the optimal position of outriggers on the base of the structural roof deflection. In the engineering practice, however, inter‐story drift is the most important target to control the design of tall building structures. This paper investigates the theoretical method of inter‐story drift‐based optimal location of outriggers. A Matlab program is written to perform the parameter analysis of optimal location of outriggers. Take a 240‐m tall building for a target building, the optimal location of one to three sets of outriggers under wind and earthquakes is obtained and can be utilized for the structural preliminary design of tall buildings. Copyright © 2015 John Wiley & Sons, Ltd.     

非线性基础隔震结构复振型反应谱设计方法

采用铅芯橡胶支座、弹性滑板支座或摩擦摆支座的基础隔震结构,在利用反应谱方法进行设计时,需要考虑支座的非线性特征.在传统非线性振动分析平均方法或慢变振幅法中引入激励随机性,以等效线性系统和原非线性系统势能和阻尼耗能相等为原则,提出了基于能量平衡的随机等效线性化方法.在该方法中,等效刚度和等效阻尼系数表达为振动幅值的期望,...     

Evaluation and refinement of closely spaced buildings’ performance under near-fault ground motions

This paper investigates the seismic behaviour of closely spaced fixed-base and isolated building structures in near-fault (NF) zones. Seismic pounding of fixed-base structures is considered at different heights, being from one or both opposite sides and at different seismic gap width. The response evaluation results of fixed-base buildings drive towards providing limited, but adequate, seismic gaps to perform seismic isolation. This aims at reducing structural responses with no seismic pounding under limited gaps, minimising the possible damage repair and diminishing the needed maintenance works due to strong NF earthquakes. To achieve that untraditionally, the paper presents a recently proposed seismic isolation system, named roll-in-cage (RNC) isolator, as a non-traditional solution to avoid direct seismic pounding of isolated buildings with their surrounding adjacent structures. It was found that the RNC isolator’s buffer mechanism is able to draw down any possible pounding of the isolated superstructure to be within the isolator solid limits. This entirely prevents direct structure-to-structure pounding but on the account of amplifying its acceleration and drift responses. However, such amplified responses might lead to only minor or moderate structural damage under sever NF earthquakes with 1.20g peak ground acceleration. Nevertheless, such damage could be avoided entirely using stiffer RNC isolators to achieve reduction of seismic response up to 69.0% under the same severe loading conditions and limited seismic gaps with no seismic pounding. Consequently, the RNC isolator could be an efficient solution for aseismic design in NF zones considering limited seismic gaps.     

Effect of soft‐storey mechanism caused by infill elimination on displacement demand in nonlinear static procedure using coefficient method

In recent earthquakes, many buildings have been damaged due to the soft‐storey mechanism failure. The seismic design codes for buildings do not contain enough criteria to predict the real displacement of such buildings. This paper focuses on evaluating the nonlinear displacement of buildings that fail in soft‐storey mechanism form. Results show that the nonlinear static procedure with coefficient method, which is described in Chapter 3 of ASCE/SEI 41‐06, does not have sufficient accuracy for estimation of structure displacement demand in such buildings. In this paper, the coefficient methodology is used for evaluating the target displacement for 5‐storey, 8‐storey and 15‐storey special moment resisting steel frames. For this purpose, dynamic nonlinear time‐history analysis has been applied for the mentioned structures having a soft‐storey mechanism failure form. The numerical results of storey displacement and interstorey drift were compared with those values obtained from the coefficient method described in Chapter 3 of ASCE/SEI 41‐06. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic response of mega buckling‐restrained braces subjected to fling‐step and forward‐directivity near‐fault ground motions

Special characteristics of earthquakes in the near‐fault regions caused failures for many modern‐engineered structures. Fling‐step and forward‐directivity are the main consequences of these earthquakes. High‐amplitude pulses at the beginning of the seismograph have been obviously presented in forward‐directivity sites. These pulses have high amount of seismic energy released in a very short time and caused higher demands for engineering structures. Fling‐step is generally characterized by a unidirectional large‐amplitude velocity pulse and a monotonic step in the displacement time history. These monotonic steps cause residual ground displacements that are associated with rupture mechanism. In this paper, the seismic performance of steel buckling‐restrained braced frames with mega configuration under near‐source excitation was investigated. Fourteen near‐fault records with forward‐directivity and fling‐step characteristics and seven far‐faults have been selected. Nonlinear time‐history analyses of 4‐story, 8‐story, 12‐story and 15‐story frames have been performed using OpenSees software. After comparing the results, it is shown that, for all frames subjected to the selected records, the maximum demand occurred in lower floors, and higher modes were not triggered. Near‐fault records imposed higher demands on the structures. The results for near‐fault records with fling‐step were very dispersed, and in some cases, these records were more damaging than others. Copyright © 2014 John Wiley & Sons, Ltd.     

Adaptive fuzzy controller for active tuned mass damper of a benchmark tall building subjected to seismic and wind loads

Active tuned mass dampers (ATMDs) are one of the most effective solutions for mitigation of destructive effects of earthquakes and strong winds in tall buildings. In order to achieve optimal performance, these systems are designed and tuned to mitigate effect of either wind or earthquake excitation. However, due to different frequency contents and intensities of wind and earthquake excitations, which will cause contrasting structural modes stimulation, the ATMD designed for one of these disturbances may not work optimally for the other one. This paper addresses a methodological simulation approach for adaptive control design of ATMDs in tall buildings located in regions with high level of seismic activity and recurrent strong winds. For this purpose, a multi‐objective adaptive genetic‐fuzzy controller is proposed for the control of an ATMD of a benchmark 76‐story building subjected to wind load and earthquake disturbances. Simulation results reveal that the optimal ATMD designed for earthquake disturbance does not work adequately for wind load disturbance and vice versa. Furthermore, the proposed adaptive controller has superior performance in suppressing base shear and inter‐story drifts induced by wind load and earthquake excitations. Copyright © 2013 John Wiley & Sons, Ltd.     

A new pushover procedure for two‐way asymmetric‐plan tall buildings under bidirectional earthquakes

Conventional pushover analyses despite of extensive applications are unable to estimate the general responses of asymmetric‐plan tall buildings because of ignoring the effects of higher modes and torsion. A consecutive modal pushover procedure is one of the recent nonlinear static pushover procedures that used to analyse the seismic response of one‐way asymmetric‐plan tall buildings under one‐directional seismic ground motions. In this paper, a modified consecutive modal pushover procedure (MCMP) has been proposed to estimate the seismic demands of two‐way asymmetric‐plan tall buildings under two horizontal components of earthquakes simultaneously. The accuracy of the MCMP procedure is evaluated using different buildings and comparing with the results of FEMA (Federal Emergency Management Agency) procedures, the practical modal pushover procedure and nonlinear time history analyses as an exact solution. The results show the proposed MCMP procedure is able to estimate the displacements and storey drifts accurately and introduces a great improvement in predicting the plastic hinge rotations. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic response control of base‐isolated buildings using multiple tuned mass dampers

Seismic response of a base‐isolated building equipped with single tuned mass damper (STMD), multiple tuned mass dampers (MTMDs), and distributed multiple tuned mass dampers (d‐MTMDs) under real earthquake ground motions is investigated. Numerical study is carried out using analytical models of five‐, 10‐, and 15‐storey base‐isolated buildings equipped with the STMD, MTMDs, and d‐MTMDs. The buildings are modeled as shear‐type structure with a lateral degree of freedom at each floor level, and the buildings are isolated using the laminated rubber bearing, lead‐core rubber bearing, friction pendulum system, and resilient‐friction base isolator. The coupled differential equation of motion for the buildings are derived and solved in the incremental form using Newmark's step‐by‐step method of integration. From the numerical study conducted, it is concluded that installing a tuned mass damper at each floor level of a base‐isolated building reduces the structural response in terms of top floor acceleration and bearing displacement. It is found that installing the MTMDs and d‐MTMDs are significantly beneficial in reducing top floor acceleration as compared with the STMD. Further, almost comparable reduction in the bearing displacement could be obtained by installing the STMD, MTMDs at top, and d‐MTMDs in the base‐isolated buildings. The d‐MTMDs are more beneficial as compared with the STMD and MTMDs as otherwise huge controller mass can now be divided and distributed on different floor levels.     

Model‐Based Multi‐input,Multi‐output Supervisory Semi‐active Nonlinear Fuzzy Controller

Abstract: The authors recently proposed a new multi‐input, single‐output (MISO) semi‐active fuzzy controller for vibration control of seismically excited small‐scale buildings. In this article, the previously proposed MISO control system is advanced to a multi‐input, multi‐output (MIMO) control system through integration of a set of model‐based fuzzy controllers that are formulated in terms of linear matrix inequalities (LMIs) such that the global asymptotical stability is guaranteed and the performance on transient responses is also satisfied. The set of model‐based fuzzy controllers is divided into two groups: lower level controllers and a higher level coordinator. The lower level fuzzy controllers are designed using acceleration and drift responses; while velocity information is used for the higher level controller. To demonstrate the effectiveness of the proposed approach, an eight‐story building structure employing magnetorheological (MR) dampers is studied. It is demonstrated from comparison of the uncontrolled and semi‐active controlled responses that the proposed design framework is effective in vibration reduction of a building structure equipped with MR dampers.     

Optimal design and seismic performance of Multi‐Tuned Mass Damper Inerter (MTMDI) applied to adjacent high‐rise buildings

The tuned mass damper inerter (TMDI) is an enhanced variant of the tuned mass damper (TMD) that benefits from the mass‐amplification effect of the inerter. Here, a multi‐TMDI (MTMDI) system (comprising more than one TMDI) linking two adjacent high‐rise buildings is presented as an unconventional seismic protection strategy. The relative acceleration response of the adjacent structures triggers large reaction forces of the inerter devices in the MTMDI, which in turn efficiently improve the seismic performance of the two buildings. By addressing a real project of two adjacent high‐rise buildings connected by two corridors equipped with the proposed MTMDI system, the displacement‐, interstory drift‐, and acceleration‐based parametric optimizations are separately performed by employing Nondominated Sorting Genetic Algorithm II (NSGA‐II) under 44 ground motions from the FEMA P695 far‐field record set. It is found that the frequency content of the seismic input has strong impact on the MTMDI mitigation performance. Adopting realistic mass ratio constraints, the optimally designed MTMDI outperforms both conventional MTMD and single TMDI in acceleration control, while it is not much effective in mitigating the displacement response due to the highly flexible nature of the high‐rise buildings, in contrast to other literature studies generally focused on low‐to‐medium rise buildings.     

Design and compilation of specifications for a modular‐prefabricated high‐rise steel frame structure with diagonal braces. Part I: Integral structural design

Prefabricated steel structures have certain obvious advantages, that is, rapid construction, industrial production, and environmental protection. Although prefabricated structures have been applied in a number of countries in the world, in most cases, these structures are suitable only for low‐rise buildings, and their applications in high‐rise buildings are nota\bly rare. This paper proposes a new type of prefabricated steel structure called the modular‐prefabricated high‐rise steel frame structure with diagonal braces. Based on the T30 building, which is a hotel building with 30 storeys above the ground, the mechanical properties, failure mode, failure mechanism, and elastic–plastic development laws of the structure were studied via elastic and elastic–plastic design and analyses under various load cases and combinations. The analysis of the internal force and displacement response with frequent earthquakes was performed using the response spectrum and elastic time‐history methods, and an analysis under rare earthquakes is performed via static elastic–plastic pushover analysis. This paper summarizes the elastic and elastic–plastic structural design methods and process. This study provides important references for the design of this kind of modular‐prefabricated high‐rise steel structure, and the design method has been compiled into a design specification named Technical Specifications for Prefabricated Steel Frame Structure with Diagonal Bracing Joints.     

带抗拉装置高层隔震结构振动台试验研究

西昌（9度区）某高层基础隔震结构,其上部为框架-核心筒结构,总高度为58.3m（不计入隔震层）,隔震层采用铅芯橡胶隔震支座。为研究该隔震结构的抗震性能及检验带抗拉装置隔震支座的有效性,进行了缩尺比为1/15模型的模拟地震振动台试验。结果表明,隔震层降低了上部结构的加速度反应,隔震层上加速度放大系数小于0.5,可满足抗震设防烈度降低一度的设计目标;隔震结构的位移集中在隔震层,上部结构的层间位移较小,层间位移角满足规范层间位移角限值要求;隔震层力-位移滞回曲线较为饱满,具有良好的耗能能力。罕遇地震作用下,支座出现拉应力,说明隔震结构在高烈度地震作用下存在倾覆的可能性。对角部隔震支座加装抗拉装置后,再次进行振动台试验,结果表明,抗拉装置不会对结构水平向动力特性及支座在正常受压状态下的竖向运动和水平向运动产生显著影响,通过对比证明了其在隔震支座受拉情况下提供的有效抗拉作用。     

Collapse behavior evaluation of asymmetric buildings subjected to bi‐directional ground motion

This paper discusses the collapse behavior of low‐rise plan‐asymmetric buildings under bi‐directional horizontal ground motions and utilizing strength and stiffness degrading nonlinear models. For this purpose, three‐dimensional three‐story and six‐story reinforced concrete frame buildings with uni‐directional mass eccentricities equal to 0% (symmetrical), 10%, 20% and 30% are subjected to nonlinear static (pushover) as well as incremental dynamic analyses using a set of far‐field two‐component ground motions and their performance are assessed on the basis of the safety margin against collapse and its probability of occurrence. Comparison of the collapse margin ratios as well as the fragility curves demonstrates significant reduction of the collapse‐level ground motion intensity with increasing eccentricity in plan. Results also indicate that current seismic design parameters including the response modification (R), overstrength (Ω) and ductility (μ) factors are not appropriate for buildings with high levels of plan eccentricity. Buildings with high values of plan eccentricity do not meet the design target life safety performance level on the basis of the calculated probability of collapse and safety margin against collapse. It appears that re‐evaluation of their design parameters is necessary. Copyright © 2015 John Wiley & Sons, Ltd.